Farhad Rahimi Klie

Posted on Feb 6

Redux Explained in Depth

#redux #reduxtool #react #frontend

State management is one of the hardest problems in front-end development. As applications grow, keeping data consistent across components becomes complex, error-prone, and difficult to debug. Redux was created to solve this exact problem with a strict, predictable architecture.

This article explains Redux from the ground up, including why it exists, how it works internally, and how its architecture enforces predictable state management.

What Is Redux?

Redux is a predictable state container for JavaScript applications.

It is most commonly used with React, but it is framework-agnostic and can work with Angular, Vue, Svelte, or even vanilla JavaScript.

Redux does not manage UI.
Redux manages application state in a centralized, structured, and predictable way.

Why Redux Exists (The Problem It Solves)

Before Redux, applications suffered from:

Prop drilling (passing data deeply through components)
Multiple sources of truth
Unclear state mutation
Difficult debugging
Inconsistent UI behavior

As apps scale, state becomes:

Shared
Mutable
Hard to trace

Redux enforces rules that eliminate these problems.

Core Principles of Redux

Redux is built on three fundamental principles.

1. Single Source of Truth

The entire application state lives in one JavaScript object called the store.

UI → Store → UI

Benefits:

Easy debugging
Centralized data
Time-travel debugging
State persistence

2. State Is Read-Only

The state cannot be modified directly.

The only way to change state is by dispatching an action.

dispatch(action)

This rule prevents:

Accidental mutations
Hidden side effects
Unpredictable behavior

3. Changes Are Made With Pure Functions

State changes are handled by reducers, which are pure functions.

A reducer:

Takes previous state
Takes an action
Returns a new state

(state, action) => newState

No mutations. No async logic. No side effects.

Redux Architecture Overview

Redux has five core building blocks:

Store
State
Actions
Reducers
Middleware

Let’s break each one down.

1. Store

The store is the heart of Redux.

It:

Holds the entire state tree
Allows access to state
Allows state updates via dispatch
Registers listeners

const store = createStore(reducer)

The store exposes:

getState()
dispatch(action)
subscribe(listener)

2. State

The state is a plain JavaScript object.

Example:

{
  user: {
    id: 1,
    name: "Alex"
  },
  cart: {
    items: [],
    total: 0
  }
}

Important rules:

State is immutable
State is serializable
State shape is intentional and explicit

3. Actions

An action is a plain object that describes what happened.

{
  type: "ADD_TODO",
  payload: "Learn Redux"
}

Rules:

Must have a type
Must be serializable
Should describe events, not logic

Actions do not change state.

Action Creators

Functions that return actions:

function addTodo(text) {
  return {
    type: "ADD_TODO",
    payload: text
  }
}

4. Reducers

Reducers are pure functions that calculate the next state.

function todoReducer(state = [], action) {
  switch (action.type) {
    case "ADD_TODO":
      return [...state, action.payload]
    default:
      return state
  }
}

Rules of reducers:

Never mutate state
No async code
No side effects
Always return something

Combining Reducers

Large apps split reducers by domain:

combineReducers({
  user: userReducer,
  cart: cartReducer
})

Each reducer manages its own slice of state.

5. Middleware

Middleware extends Redux with custom behavior between:

dispatch → reducer

Common use cases:

Logging
Async requests
Error handling
Analytics

Redux Thunk (Async Logic)

Redux itself is synchronous.

Thunk allows dispatching functions:

dispatch((dispatch) => {
  fetchData().then(data => {
    dispatch({ type: "SUCCESS", payload: data })
  })
})

Flow:

Action dispatched
Middleware intercepts
Async work happens
Real action dispatched

Redux Data Flow (Step by Step)

Redux has one-way data flow:

UI triggers an event
Action is dispatched
Middleware (optional)
Reducer calculates new state
Store updates state
UI re-renders

UI → Action → Middleware → Reducer → Store → UI

This predictability is Redux’s biggest strength.

Why Redux Is Predictable

Redux enforces:

No hidden mutations
No bidirectional data flow
Explicit state changes
Centralized logic

Every state change can be:

Logged
Replayed
Debugged
Tested

Redux vs Local State

Local State	Redux
Component-scoped	Global
Simple	Structured
Hard to share	Easy to share
Quick	Scalable

Redux is not for every app.

Use Redux when:

State is shared widely
State logic is complex
Debugging matters
App is large or growing

Modern Redux (Redux Toolkit)

Today, Redux Toolkit (RTK) is the recommended way to use Redux.

It:

Reduces boilerplate
Uses Immer internally
Enforces best practices
Includes middleware by default

createSlice({
  name: "counter",
  initialState: 0,
  reducers: {
    increment: state => state + 1
  }
})

RTK keeps Redux powerful without complexity.

Common Misconceptions About Redux

❌ Redux is only for React
❌ Redux replaces React state
❌ Redux is outdated
❌ Redux is always complex

✔ Redux is a state architecture, not a UI tool
✔ Redux complements component state
✔ Redux is still actively maintained
✔ Complexity depends on usage

When You Should NOT Use Redux

Avoid Redux if:

App is small
State is local
No shared logic
No complex updates

Redux is a tool, not a requirement.

Final Thoughts

Redux is not just a library — it is a state management philosophy.

It enforces:

Discipline
Predictability
Explicit data flow
Long-term maintainability

When used correctly, Redux scales better than almost any alternative.

If your application needs reliable, debuggable, and scalable state management, Redux remains one of the strongest architectural choices available.

DEV Community